A typical liquid filter has a tank divided horizontally into an upper tank and a lower compartment. The upper tank receives dirty liquid to be filtered. A perforated plate or porous septum/screen separates the upper tank and the lower compartment. Filter media, such as a paper web, is driven across the perforated plate. A vacuum in the lower compartment induces liquid flow from the upper tank through the filter media and the perforated plate into the lower compartment. Such filters are used in connection with the filtration of machine tool liquid coolant in which cutting chips and other solid debris are filtered from the coolant by the filter media prior to being recirculated back to machine tools.
Filter media can take the form of disposable media (paper or roll) or a permanent or recleanable media belt. The permanent media belt is indexed periodically through the tank as the belt becomes clogged to advance a fresh segment onto the perforated plate. Each indexed segment is cleaned and recirculated back under tank and then over the perforated plate. Alternatively, a disposable media strip can be indexed periodically, each segment of which is collected for disposal after use. Both permanent and disposable media may be used in combination with the disposable media overlying the permanent media.
Filter media is often driven by a drag conveyor having a pair of spaced apart chain loops connected by flights extending across the width of the media. The flights carry the removed solids filtered by the filter media such as machining chips out of the tank.
The drag conveyor frictionally drives the permanent media belt. The weight of the chain loops and the flights of the drag conveyor bears on edges of the media belt to seal the same and create a frictional engagement to carry the media belt through the tank as the conveyor is periodically indexed. Only frictional engagement is used with disposable media.
A problem with frictionally driving the permanent media belt is that it is difficult to remove or replace the belt if it breaks during use. Another problem is the uneven wear on the permanent media belt.
What is needed is another pair of drive loops for driving the permanent media belt independently of the pair of drive loops driving the drag conveyor.